Hochschule für Architektur, Bau und Geomatik FHNW
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Bereich: Suchergebnisse
Publikation Comparing Q347 development and regionalization using recent data in two Swiss cantons(09.11.2024) Dups, Yanick; Lebrenz, HenningIn Switzerland, low flows are characterized by the discharge level corresponding to a 95% exceedance probability on a ten-year average flow duration curve, referred to as Q347. This threshold not only has significant implications for planning but also requires authorities to adjust the operation of relevant infrastructure to mitigate ecological impacts on watercourses. The value of Q347 can be determined from a flow duration curve if a discharge time series of at least ten years is available. However, for smaller catchments such time series are typically unavailable, necessitating the regionalization of Q347 values. In Switzerland, multiple linear regression has been established to estimate the area-specific discharge q347 for ungauged basins. The primary objective of this study was to regionalize Q347 values for small, ungauged catchments (383 in the Canton of Solothurn and 9'034 in the Canton of Zürich) each with an area of less than 100 km². Daily discharge, precipitation, and temperature time series were collected for a 30-year study period from 1990 to 2020 from 56 gauged catchments in Solothurn, and similarly for a ten-year study period from 2013 to 2023 in Zürich, focusing on catchments smaller than 500 km² surrounding the target areas. A total of 30 “static” parameters delineating geometry, topography, geology, land use, and drainage along with nine “climatic” parameters describing temperatures, precipitation distributions, and potential evapotranspiration were defined and computed to characterize both gauged and ungauged catchments. The temporal variability of low flow events was then analysed for observed catchments in the two study areas. Over the past 30 years, the frequency of low flow events below the threshold has systematically increased, while the ten-year Q347 values for these catchments have decreased during the same period. Three multiple linear regression methods were developed and implemented to be coupled with two adjustment techniques supplementing truncated discharge time series. Validation of the proposed models showed reduced errors and increased linear correlations between estimated and observed values compared to standard models. Notably, a spatially more homogeneous yet catchment-specific distribution of estimated values is observable. The proposed models yielded promising results, particularly when time series remain unadjusted, or adjustment is done using the Antecedent Precipitation Index (API) combined with the flow duration curve of a donor basin (Ridolfi et al., 2020). Using recent data for parameter selection and model fitting, especially in the Zürich study area (2013-2022), often resulted in lower Q347 values compared to standard models, reflecting an adaptation to current climatic trends.06 - PräsentationPublikation Fliessgewässer im Nordwestschweizer Jura in Zeiten der Trockenheit und des Klimawandels(Geographisch-Ethnologische Gesellschaft Basel, 2022) Lüscher, Peter; Weingartner, Rolf; Pavia Santolamazza, Daniela; Lebrenz, HenningTrockenheit und Niedrigwasser sind aus hydrologischer Sicht der Gewässer eine der grössten Herausforderungen in der Schweiz. In diesem Beitrag werden die Niedrigwasserverhältnisse im Nordwestschweizer Jura untersucht. Dabei steht die Frage der heutigen und zukünftigen Trockenheitsanfälligkeit im Mittelpunkt. Die Resultate belegen, dass signifikante Unterschiede zwischen Ketten- und Tafeljura bestehen, wobei die Fliessgewässer im Tafeljura insgesamt trockenheitsanfälliger sind. Gelingt es nicht, die Treibhausgasemissionen wirkungsvoll zu begrenzen, wird die Trockenheitsanfälligkeit gemäss dem Szenario ohne Massnahmen (RCP 8.5) bis Ende des Jahrhunderts deutlich zunehmen.01A - Beitrag in wissenschaftlicher ZeitschriftPublikation New estimation models for determining the Q347(17.04.2024) Dups, Yanick; Santolamazza, Daniela Pavia; Staufer, Philipp; Lebrenz, HenningIn Switzerland, low flows are described by the five percent quantile denoted by Q347. This threshold value not only has consequences for the planning, but also necessitates authorities to adjust the operation of pertinent infrastructure to mitigate ecological impacts on watercourses. Given a discharge timeseries spanning at least a ten-year period, determination of the Q347 can be done using the duration curve. Typically, said timeseries are not available for smaller catchments necessitating the estimation of the threshold value Q347. In Switzerland, the utilization of multiple linear regression has been established to estimate the area-specific discharge q347. The primary objective of these investigations is to estimate the Q347 value for 383 ungauged catchments in the Canton of Solothurn, each covering an area less than 100 km². Daily discharge, precipitation and temperature timeseries ranging from 1990 to 2020 were collected from 56 gauged catchments smaller than 500 km² surrounding the target area. 30 “static” parameters delineating geometry, topography, geology, land use, and drainage along with nine “climatic” parameters describing temperatures, precipitation distributions, and potential evapotranspiration were defined and computed to characterize gauged and ungauged catchments. Alongside comparing three regression methods, coupled with two adjustment techniques supplementing truncated discharge timeseries, three parameter selection methods are evaluated. The validation of the proposed models shows reduced errors and increased linear correlations between estimated and observed values compared to currently applied models. Notably, a spatially more homogeneous yet catchment-specific distribution of estimated values is observable. Particularly when timeseries remain unadjusted or adjustment is done using the Antecedent Precipitation Index (API) and the flow duration curve from a donor basin (Ridolfi, E.; Kumar, H.; Bárdossy, A., 2020), the proposed models yield promising results. Furthermore, the temporal variability of low flow events for the glacier-free catchments in the study area has been analysed. The frequency of low flow events below the threshold systematically increased over the last 30 years, while the 10-year Q347 value of said catchments has systematically decreased in the same period. The increase in low flow days leads to large errors in the estimation of the Q347 value, especially when its estimation is based on truncated timeseries. As further changes in runoff behaviour are to be expected due to climate change, extending the definition of "low flow" to include event duration and intensity alongside a fixed threshold value could offer a more suitable description.06 - PräsentationPublikation Analysis of the resolution of precipitation data required to obtain robust results from a hydrodynamic sewer network model(19.04.2024) Rabiei, Ehsan; Hoppe, Holger; Lebrenz, HenningThe need for precipitation data for calibrating hydrodynamic sewer network models is often compromised by using the nearest available rain gauges to study area. Due to the scarcity and irregular locations of the rain gauges, this way of satisfying the need for precipitation data can lead to incorrect conclusions with respect to the temporal and spatial patterns of precipitation, depending on the location of the rain gauges in the study area. Recent developments in the field of precipitation measurement by means of weather radar data open up new possibilities for the use of such data sources in hydrodynamic sewer network models. Even though weather radar provides precipitation information with a high temporal and spatial resolution, the raw radar data contains several sources of error and is inaccurate. The radar data are therefore often corrected and merged with ground measurements. The main objective of this study is to investigate the resolution of precipitation data required to obtain robust results in a hydrodynamic channel network model. The study area is a small catchment close to Munich in Bavaria, Germany. Data from the Isen weather radar station of the German Weather Service (DWD), which is located around 33 km from the study area, was used. Following the objectives of this study, various weather radar data products were processed in order to be used as input for a hydrodynamic sewer network model. The data with a temporal resolution of 5 minutes to 1h and a spatial resolution of 250 m x 250 m up to 1.000 m x 1.000 m form the basis for creation of datasets to be investigated. It has been observed that the use of high-resolution precipitation data leads to better model results, especially when the data is merged with rain gauges. However, it should be noted that the quality of the model results does not decrease linearly when the resolution of the precipitation data is reduced.06 - PräsentationPublikation Semi- or fully automatic drainage regulation as a mean to recharge groundwater(17.04.2024) Venuleo, Sara; Unrau, Silas; Staufer, Philipp; Lebrenz, HenningClimatic change is decreasing water availability, all over the world. Regions which never faced water scarcity need to adapt their practises to face more frequent and severe droughts periods. Among others, agriculture is one of the sectors that will face the consequences of water scarcity. Indeed, while water availability decreases, the use of water for irrigation purposes becomes questionable. In many regions in Europe, cultivated areas have a sub-surface drainage system, which ensures that crops do not face water stress due to excessive soil water content. These drainage systems convey the water infiltrating during rainfall events to surface channels, reducing the natural water table recharge. Introducing drainage regulations units in existing drainage systems represent a mean to increase the soil water retention and, consequently, a mean to increase the natural water table recharge while decreasing the need of irrigation and while helping to reduce peak flow during intense rainfall events. Moreover, controlled drainage management can reduce the amount of Nitrogen and Plant Protection Products (PPP) discharged into surface waters. Given its environmental benefits, drainage water management is today an official conservation practice in the USA and the Conservation Practice Standard 554 (code 554) has been published by the United States Department of Agriculture to inform, advice and guide potential users of this practise. Drainage control units can be simple structures retrofitted in existing drainage networks outlets. They can consist of sliding weir systems or of a flashboard with adjustable height and they can be operated manually or automatically. In the present study an automatic drainage control unit has been developed and operated in a laboratory prototype. The objective of our experiment was understanding which technical and practical difficulties are faced in the use of a drainage control unit and thus which issues hinder its spread among farmers. Particular attention was given to possible issues associated with sedimentation.06 - Präsentation
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